Nowadays, the application of more and more electric and electronic devices aggravates the harmonic pollution of the power grid, in order to better reduce the harmonic waves, the PFC circuit is widely applied. Meanwhile, the PFC circuit also develops towards a direction of high efficiency and high power density.
In multitudinous PFC circuits, a Critical-conduction Mode (CRM) PFC circuit is extensively applied. With the topology of the totem-pole-type bridgeless PFC circuit as an example, when working in a critical-conduction mode, it can realize Zero voltage switch (ZVS) or Valley switch (VS) in the full alternating current input range and full load range, and also can simultaneously meet the requirements of high power density and high efficiency.
FIG. 1 is a structure diagram of a critical-conduction bridge PFC circuit for detecting inductor current of the PFC circuit in the related art. As shown in FIG. 1, the critical-conduction bridge PFC circuit includes at least two bridge arms connected in parallel between a first connection point A and a second connection point B, herein a first bridge arm includes two diodes connected in series in the same direction, and a second bridge arm includes two diodes connected in series in the same direction. The critical-conduction bridge PFC circuit also includes one PFC inductor, there is one switch tube S1 between a third connection point C and the second connection point B, there is one diode D5 between the third connection point C and a fourth connection point D, and there are a filter capacitor C0 and a load R0 also connected in parallel between the fourth connection point D and the second connection point B.
FIG. 2 is a structure diagram of a totem-pole-type bridgeless PFC circuit for detecting inductor current of the PFC circuit in the related art. As shown in FIG. 2, the totem-pole-type bridgeless PFC circuit includes at least two bridge arms connected in parallel between a first connection point A and a second connection point B, herein a first bridge arm includes two switch tubes or diodes connected in series in the same direction, and a second bridge arm includes two switch tubes connected in series in the same direction. The totem-pole-type bridgeless PFC circuit includes one PFC inductor, and a filter capacitor C0 and a load R0 also connected in parallel between the first connection point A and the second connection point B. When the input voltage is in the positive half cycle, a diode D2 is always conductive, a switch tube S2 is closed, a switch tube S1 is disconnected, and at this point the current on an inductor L increases from zero to store energy; after the above energy storage process ends, the switch tube S2 is disconnected, the switch tube S1 is closed, and at this point the current on the inductor L decreases from the peak value to release energy. When the input alternating voltage is in the negative half cycle, a diode D1 is always conductive, the switch tube S1 is closed, the switch tube S2 is disconnected, and at this point the current on the inductor L increases from zero to store energy; after the above energy storage process ends, the switch tube S1 is disconnected, the switch tube S2 is closed, and at this point the current on the inductor L decreases from the peak value to release energy.
However, in the process of applying the critical-conduction bridge PFC circuit and the totem-pole-type bridgeless PFC circuit in the related art to perform practice and research, the critical-conduction mode power factor correction circuit is required to timely and accurately obtain an inductor current signal which is used for loop control or implementing the inductor current protection function, but how to obtain the inductor current signal is a problem required to be urgently solved by the researchers.